The candidate is in the Department of Surgical Research of Children's Hospital, Boston, headed by Dr. Judah Folkman. The candidate has previously been involved in the discovery of novel small molecular weight anti-angiogenic compounds as well as applications of angiogenesis inhibitors in the laboratory of Dr. Robert D'Amato. The long- term career objectives are to investigate the biology of angiogenesis and stromal interactions in cancer and in physiologic development. Identification of critical molecules that participate in regulating the angiogenic balance will lead to new therapeutic targets and strategies for cancer therapy. As part of this objective, the angiogenic balance in mouse models of human tumor dormancy will be investigated. In this research plan, it is hypothesized that changes in the net balance of stimulators and inhibitors of angiogenesis govern the transition from dormancy to expansion. To explore this hypothesis, the first specific aim is to develop models for human tumor dormancy using hypovascular tumors which fail to grow progressively in experimental animals but persist as viable, microscopic foci. These tumors will be characterized for microvessel density, proliferation, and apoptosis. Dormant tumors will be transfected with fluorescent proteins to facilitate their identification in vivo for subsequent isolation and analysis of gene expression. In the second specific aim, tumors will be rescued from dormancy by expressing genes that are known to perturb the angiogenic balance. Tetracycline regulated expression, combined with fluorescent imaging, will be used to study the changes in the angiogenic balance that occur in the transitions between dormancy, escape, and regression. Finally, novel regulators of angiogenesis will be identified by comparing the profile of molecules that are upregulated (potential stimulators) or downregulated (potential inhibitors) upon rescuing tumors from dormancy. Differentially expressed factors at the protein level will be analyzed by 2D gel electrophoresis combined with mass spectrometry, or at the level of message by microarray profiling and analysis of gene expression. Their role in angiogenesis will be determined by overexpressing or inhibiting their expression as in aim 2. An understanding of the interplay between angiogenic and antiangiogenic activities will yield insight into the biological basis for human tumor dormancy, and may also uncover new molecules for the treatment of cancer.